Theme Data problem, fix makes no sense

One of my custom themes stopped pulling in the Theme data from the style.css on the ‘Manage Themes’ page for no apparent reason.

As a test:

1. I opened the offending style.css and removed all data from it except for the theme data at the top – this had no effect.
2. I then opened up the style.css from Twenty Eleven and copied and pasted the entire contents into the style.css of the theme that had stopped pulling the data – this also had no effect.
3. Finally, I copied all of the contents from the style.css of the theme that had stopped pulling the theme data, and copied that into the style.css of Twenty Eleven. I then deleted the style.css from the offending theme and copied the style.css from Twenty Eleven (that was actually the same exact contents from the theme that wasn’t pulling theme data) into that theme. This worked.

Anybody have any idea what is going on here? This doesn’t make any sense to me. Another one of my themes is doing the same thing now and I would like to understand what the problem actually is. Thanks!